Rowing is one of the most efficient forms of exercise. The oarsman sits on a movable seat and has his feet secured to a footrest attached to the hull of the boat. The sliding action of the seat enables the oarsman to pull the oars through a stroke with the large muscles of the upper leg, the upper and lower back muscles, and the muscles of the arms and shoulders. After completing a stroke the oarsman lifts the oars from the water and returns to the original position by pulling himself forward on the sliding seat with the muscles of the abdomen and rear thigh. The movement of the boat is resisted by the drag force of the water on the hull.
Many devices have been designed for rowing exercise. Most of these devices consist of a stationaryfootrest attached to a frame, a sliding seat mounted on the frame, and handles to be pulled by the user against resistance to simulate the movement and resistance of the oars of a boat. Some devices employ a seat immoveably attached to a frame with a movable footrest. Portable rowing exercise devices have been designed with springs or rubber strips for resistance.
The most desirable rowing exercise devices use a resistance means which provides a fairly constant resisting force for the entire stroke, and a means of disengaging the resisting force for the return. Cylinders, fans, springs, elastic or frictional resistance devices can be used to provide the resisting force with an appropriate clutch, ratchet or valve for disengaging it (springs and elastics are self disengaging). Each kind of resistance means has drawbacks: force exerted by a spring is proportional to the spring's extension, and hence would not be constant over a stroke; friction means heat with intensive use, causing the resistive force to lessen, or "fade"; fans exert a force proportional to the volume of air moved by the fan, and thus, for intensive training, a fan too large for a portable device would be necessary; hydraulic or pneumatic cylinders, although better suited for intensive training, are unduly expensive and also too large for a portable device. Any invention that can adapt friction or fan exercisers to the requirements of high intensity training in a portable rowing exerciser would be a welcome advancement in the art.